Since the end of the 1980s, the code division multiple access (CDMA) technology has been used in the field of the digital mobile communication. Because of the efficiency in frequency use and capability of rejecting interference, CDMA technology has become an excellent choice of a mobile communication system. With the development of the mobile communication technology and the increasing demand of communication, the research and development has focused on the third generation of a mobile communication system. It is a common knowledge that the CDMA technology is used in the third generation of the mobile communication system. Currently, three mechanisms have been accepted as a selection pool for an air interface of the International Mobile Telecommunications for the year 2000 (IMT-2000). They are: wide-band CDMA (WCDMA), CDMA2000 and TD-SCDMA, respectively.
In a WCDMA cellular system, channel address codes interact with each other. The effects are two folds: the first one is that any one of the channels will be interfered by the other channels with different address codes, that is the interference caused by multiple access; and the second one is that the reception of the channels with a distance near a receiver is interfered more seriously than the reception of the channels with a distance far from the receiver, thereby causing the strong signals at the near-end to cover the weak signals at the far-end, i.e. the near-far effect. A WCDMA system is a self-interfering system, and any accumulation of various kinds of interference reduces the capacity and quality of the system. A plurality of key technologies, including power control, diversity transmission, and the like, are employed in a WCDMA digital mobile communication system to implement the advantages of high capacity and high quality. Reducing the transmission power and interference has become the key features of WCDMA technology.
Paging function is one of the basic functions in a communication system.
When user equipment is in a cell dedicated channel state for a connection mode (i.e. a CELL_DCH state) or in a cell forward access channel state (i.e. a CELL_FACH state) in a WCDMA system, PAGING TYPE 2 is transmitted downwardly by a base station via a dedicated control channel.
When the user equipment is in an idle mode, in a connection mode of a cell paging channel state (i.e. a CELL_PCH state), or in a user registering area paging channel state (i.e. a URA_PCH state), it is required to use a paging control channel (PCCH) to implement the paging function. Paging information of PAGING TYPE 1 is transmitted downwardly, and the paging channel (PCH) is mapped into a transmission channel. It is borne by a subsidiary common control physical channel (S-CCPCH) in a physical layer, and the user equipment is informed of whether a paging is present or not by a paging indication channel (PICH) of the physical layer.
The paging indication channel (PICH) and the S-CCPCH for bearing PCH information are associated with each other and have a relationship according to the time sequence, as shown in FIG. 1. If a paging indicator Pq in the paging indication channel (PICH) frame is set to 1, then it is indicated that the paging messages will be borne by the frame of the subsequent subsidiary common control physical channel (S-CCPCH), and that the frame of the subsidiary common control physical channel (S-CCPCH) will begin to transmit at the time τPICH after the PICH frame, wherein τPICH is defined as 7680 divisions. After the paging indication of the user equipment is retrieved by itself from the indicator of the PICH channel, the contents of the paging information is retrieved on the corresponding S-CCPCH channel. Each of the user equipment corresponds to one indicator on the PICH channel. Therefore, how many indicators in one PICH frame that will be set to 1 depends on how many paging messages of the user equipment is transmitted downwardly by the subsequent S-CCPCH channel at a time.
A plurality of complete −1 bits are used in the present transmission scheme of the paging indication channel (PICH) to indicate that the indicator is set to 1, that is, there is paging information corresponding to the user equipment; and a plurality of complete +1 bits indicate that the indicator is 0, that is, there is no paging information for the user equipment. It is assumed that a certain user equipment corresponds to the paging indicator Pq, the suffix q indicates the location of the paging indication corresponding to the user equipment, and both the base station and the user equipment obtain q by calculating based on the existing equation, for example, the one currently existed in the protocol of WCDMA system:q={PI+[((18*(SFN+[SFN/8]+[SFN/64]+[SFN/512]}))mod144)*Np/144])mod Np wherein, the parameter PI is obtained by the calculation by the high layer of the user equipment, SFN is the frame number of the system corresponding to the primary common control physical channel (P-CCPCH) at the time PICH beginning to transmit.
FIG. 2 illustrates the PICH frame structure. Each PICH frame has Np paging indicator mapping into information of 288 bits, wherein, Np=18, 36, 72, 144. The transmission of the last 12 bits of the frame is closed off to reserve for expanding the other channels. The corresponding relationship between the respective paging indicators of the PICH frame and the PICH bits (bits of the PICH frame) is shown in Table 1 as follows.
TABLE 1Number ofpaging indication ofeach frame (Np)Pq = 1Pq = 0Np = 18{b16q, . . . b16q+15} ={b16q, . . . b16q+15} ={−1, −1, . . . −1}{+1, +1, . . . +1}Np = 36{b8q, . . . b8q+7} ={b8q, . . . b8q+7} ={−1, −1, . . . −1}{+1, +1, . . . +1}Np = 72{b4q, . . . b4q+3} ={b4q, . . . b4q+3} ={−1, −1, . . . −1}{+1, +1, . . . +1} Np = 144{b2q, b2q+1} ={b2q, b2q+1} ={−1, −1}{+1, +1}
In such PICH channel transmission method, the signals are transmitted regardless of whether the paging information exists or not. +1 or −1 is decided by the user equipment from the phase of the bits of the received PICH frame, thereby deciding whether the paging information exists or not.
In the current WCDMA system, up to 8 user equipment can be paged simultaneously in one paging information. However, the paging capability of the paging indication channel PICH is much larger. Only up to 8 bits in Np paging indicators is set to 1, that is, a large part of the power used for transmitting the information is Pq=0, i.e. no paging. In this situation, not only the transmission power is wasted, but also the other users are interfered, and the system capacity is affected.